Traffic controlling apparatus



Jan. 9, 1951 G. w. BAUGHMAN 2,537,298

TRAFFIC CONTROLLING APPARATUS Filed Oct. 50, 1945 2 Sheets-Sheet l .L 1 A WQ 1/ X X 15002 TH B g- 6 in H 7 LL17 X L X J 050 M 0 LEE r-(B .DT 18000 INVENTOR HIS A TTORNE Y a 1951 cs. w. BAUGHMAN 2,537,298

TRAFFIC CONTROLLING APPARATUS Filed Oct. 50, 1945 2 Sheets-Sheet 2 W5 L *fi E: a L5 P .41

51 D5 D1 5 E 5 i 6D] I '3 I LP s Y George i l ffi aayl gi B H15 ATTORNEY Patented Jan. 9, 1951 UN ITE'D .S FAITES -Applicatin-October'30, 1945, SerialNo. 625,561

:My inventionrelates to itra'flic controlling apparatus, and -more particularly to electronic means for :detecting the presence of a railway 'car in'anextendedxstretchmf track which-means does *notdepend upon electrical contactbetween the wheels of the car and the track, rails. The ,:principal object of my inventionis to pro- .vide improved proximity detecting means tosupplement 101' to serve as-a'substitute for a railwaymrack circuitior use for'exampla-tc detect the presencecf a car :on the trackslof a :crossover which may have :a :high contact resistance due to infrequent train movements, or vto detect the presence-of lightweight vehicles 'or-of those having insulated wheels and incapablecfshunting thezusualtrack circuits, or-todetectthepresence of-cars ongrailway crossing-sor at other-locations where :the installation of track :circuits is impracticable.

vA further object of .my ,invention is to provide means vfor reliably detecting -the presence of a movable. object in a protectcdspace, .Which'means is suitable for use ,in trafiicxcontrol systems in which track circuits cannot .be .used. The apparatus .of myiinventicn isthus adapted toproyideithe equivalentof railway trackecircuit protection in systems for @the control f .non-rail traffic, and may be used .for example v.ior the detection of the presence of road vehicles on highwaysor forthe detectionof such vehicles, or of airplanes .on theground, in .airportareas.

The .apparatus .of my invention detects ,the presence of a vehicle by measuring the variation in the impedance of an. electric cir.cuitelement, suchas aloop of wiressurrounding theprotected space. An additional .o-biect .of .myinvention is the provisionof selfechecking apparatus .for this purpose, v.comprising. a Wheatstone bridge 'which, although it employs a .null* method .of Jimpedance measurement, has incorporated therein the closed .circuit principle .of operation which is..a anecessary requisite fem-safety devices of this character. In respect-to.this feature,my invention is an improvement. upon that disclosed in my United States Patent No. 2,335,487, issued,September 25, -1945, for Hot aBearine Alarms- I shall describe two :forms of :apparatus embodying my invention .and shall then point out the-.novel'features.thereofrinclaims.

'.-Referring to the .-accempanying drawin s, 1 shows one -form=of :train detecting apparatus embodying -;rny invention in which an insulated wire T1001? ;L is mounted z between the track rails i and 2| pf ran extended stretch of railway track 10 Claims. (Cl. 177-3523) about'the track .rails iwhich would be occupied by atrainin an-extended stretch ogf'track. -An electronicoscillator comprising the tube V5 "is normally energized to generate alternating current ofa frequency determinedby the inductance of loop :L, which current is modulated-at a-lowire- ,quency'rate by; an interrupter relay or code transmitter i89C!I,'-and *is amplified by a second tube V32. When the -stretch isunoccupied, the modulatedcurrent-passes through a selective filter El and is demodulated to energize .a detector :relay CD, but when a car occupies the stretch; a chan in frequency occurs and relay CD {is released. Fig.2 shows ,a second .;form of mysinvention in which'the loop L formsone arm of a Wheatstone bridge which is supplied with current ofa fixed frequency by an electronic oscillator OSC, the bridge being balancedonly when the loop is 1111- occupied to maintain a detector relay CD ener.-. gized. Fig. 3 shows :anapplication of .the train detectingapparatus of Fig. ,1-0r;2 to a specific problem, namely, that of protecting train movements over a .stretch of double track railroad containinga crossover. c

Similar reference characters :refer -.to similar parts in each of the views, and indieucfshowing the .various'sources of currentfor energizing the apparatus, I have shown onlytheir terminals, thepositive orsupply terminal being identified by the reference character B, .and the negative ,or ,common return terminal by the reference characterQ in. each instance. 7

Referring to Fig. .1, the electron tube Viis-a pentcdeof the conventional type havingits grid and plate circuitscoupled through a transformer OTntofunctionas an oscillator to generate alternatingcurrentof afrequenkzy determined by a tank:circuit coinprising the coils of transformer OT .and a condenserCi. The trachway loop L comprises two insulated wires,. one adjacent. each trackrail, connected in a closed circuit to .a winding ofntransformerOTso that the inductance due to the magnetic .field of .the loop in the .space which ,wouldbe occupied by a .car'in the stretch forms a part of the inductance tuned by condenser C! by which the frequencycf theecurrent generated by tube V! is determined.

'Usually the track rails i and .l adjacentthe p form a part of a closed track-circuit including a battery -2 and a track relay TB, .and since thevrails in practically all case are connected together through leakage paths of'lowresistance aswell as through the battery and track. relay, they iorm aclos ed circuit of relatively lowimand serves to create a magnetic fieldrin lihespace 5 15 pedance which induced :cu1?rents couldgflow,

having a magnetic field in opposition to that due to current in the loop. To avoid this the wires of the loop are transposed one or more times o place the loop in a non-inductive relation to the track circuit, as shown. A further advantage of transposing the loop is that at points some distance from the track the magnetic field of each section of the loop is neutralized to a large extent by the overlapping opposing field of the adjoining sections and the lines of force are diverted to paths which do not link with the track rails but which lie in planes parallel thereto, increasing the field strength in the space which would be occupied by a car, whereby the effect of the magnetic or conducting material of the car upon the field strength becomes proportionally greater. It follows that by measuring the inductance of the loop, as is accomplished in Fig. 1 by measuring its effect upon the frequency of the oscillations in the track circuit including transformer OT and condenser Cl, the presence of a car in the stretch of track over which the loop extends may be reliably detected since the current will have a given frequency fl only when the stretch is unoccupied.

To detect the frequency fl, an amplifier tube V2 is provided having its grid circuit connected to transformer OT in parallel with that of the oscillator tube Vl, the output circuit of tube V2 supplying current to a direct current relay CF through a rectifier R and a tuned filter circuit selectively responsive to current of the frequency fl.

Since the apparatus is intended for use at isolated wayside locations, practical considerations limit the voltage of the local battery to about 24 volts, so that the output of tube V2 is relatively small, and relay CF is of a sensitive type responsive to forces smaller than those which govern relays of conventional railway signaling types. Accordingly, the code principle is made use of to provide a safety control in accordance with accepted standards, relay CF controlling a detector relay CD of the standard typ through decod ng apparatus similar to that shown in Letters Patent of the United States No. 1,773,472, issued August 19, 1930, to Paul N. Bossart.

A code transmitter relay IBUCT of the pendulum type or the like is provided, which when energized from terminals B and C operates its contacts at a fixed rate of 180 times per minute, and r its contacts are arranged to short circuit th loop L so that the oscillation generated by the tube Vl are periodically interrupted or modulated at the same rate. Consequently when relay CF is supplied with current of frequency fl it operates its contacts percdically to supply impulses of alternately opposite polarity to the primary of a decoding transformer DT, the secondary of which supplie alternating current of the modulation frequency to a tuned decoding unit IBEJDU selectively responsive to that frequency by means of which the impulses are rectified and serve to efiect the steady energizaticn of the detector relay CD.

Relay CD therefore is steadily energized only when the loop L is unoccupied. Relay CF ceases to operate, and relay CD releases when a car or train occupies the loop and changes the frequency of the current to a value which is not passed by the filter Fl.

Referring now to Fig. 2, the oscillator 080 is to be understood to be similar to the one shown in Fig. 1 except that its frequency is not controlled by the loop. The oscillator OSC therefore constantly generates current of frequency fl, and this is supplied through a selective filter Fl to a Wheatstone bridge for measuring the inductance of the trackway loop L. One arm of the bridge includes the loop L, tuned by a condenser C2, the loop circuit including in series a periodically operating contact of the code transmitter relay lCT. The input circuit of a detector tube V3 is connected across the tuned p and a balancing impedance Z, and the output circuit of V3 includes a code following relay CF controlling a detector relay CD as in Fig. 1 already described. The circuits are so arranged that relay CF is held energized by current of frequency fl which passes through the bridge so long as the bridge is not balanced. Impedance Z is so adjusted that a balance is attained whereby relay CF is caused to release each time the contact of relay l8llCT closes, provided the measured impedance of the loop indicates that the stretch of track over which the loop extends is unoccupied. It will be seen that although the circuits for tube V3 and relay CF are deenergized when the balanced condition is being detected, the integrity of these circuits is periodically checked by the coding action and the system embodies the closed circuit principle. In the event of a fault in the circuit for relay CF, or in tube V3, or its circuits, or if oscillator OSC fails to supply energy to the bridge, relay CF will remain steadily in its released position, while a fault in the loop circuit or in its connections to the bridge will cause relay CF to remain steadily energized. It follows therefore that relay CF will be operated periodically by relay lflilCT to effect the energization of relay CD only when the loop 2 is not occupied by a train, and that relay CD will assume its released position in the event of a fault in any of the circuits.

Referring now to Fig. 3, in this view I have shown two tracks of a double track railroad provided with the usual track circuits TI and T3, each having a track battery 2 and a track relay TRI or TR3 for controlling the railway signals 2L and AR. The two main tracks are connected by a crossover comprising the hand throw switches Wl and W3, protected by the apparatus of my invention, which may be either of the forms shown in Figs. 1 and 2. Two sets of detecting apparatus designated Dl and D3, controlling two detector relays CD! and CD3 by separate track loops LI and L3 are provided for the reason that it is desirable to extend the loops to as close to the main tracks as possible in which case the passage of a train on the main track may change the inductance of the adjacent portion of the loop sufiiciently to release the detector relay. If there were only one detector relay for controlling the signals on both tracks, the release of the detector relay by a train on one main track would interrupt the circuit for the signal governing movements over the other main track.

The loops LI and L3 are transposed to place them in a non-inductive relation to the track circuit TI and T3 and they may a so be coupled by overlapping them as shown, or otherwise, so that they are in a non-inductive relation to each other.

In the arrangement shown, the track relay TRI and the detector relay CDl jointly control signal 2L, and relays TR3 and CD3 jointly control signal 4R so that the clearing of either signal is prevented in the event there is a car on the corresponding half of the crossover, that is to say, within fouling distance of the corresponding main track, even though the car fails to make contact with the track rails sufiicient to shunt the track circuit.

although 11 :have therein ishown and rdescrihed but two 'foi'm's of apparatus embodying my invention, it is understoo that tvarinu's changes and modifications may he ma'de 'therein "within "the scope of the appended c'laims zwithoutideparting from the spirit and scopaoflmy: invent-ion.

Having thus described :my :invention, :what claim isz '1. i ippara'tus Jfor detecting th-e :presence o'f :a movable *dbjedt such 1 as a vehicle in a protected area,eomprisinga l'oop -df' insulated-wire enclosing said -*are-a, a 'co'de tr-ansmitter, means contrlled by said *cod'e transmitter for azperi'otiically energizing said loop -*by alternating current at a fixed rate to create-a held of force for recurrent brief periods in the =-space which would be' occupied "-by a vehicle in said area, measuring means responsive tosa-id' alternating current forimea suring the electrical -characteiistics er said loops to detect "variations therein due to the presence of a vehicle 'in said area, a "code -following1e1ay, a det-ector relay, means controlled-by said meas 'uring means for energizing said'code following 1el'ay,"wherebysaid'relayis -maintained 'energiaed except "when" the electrroar-characteristics of the loop are :being measured "andsuch measurernent indicates that the area is not "occupied *by *a vehicle, and means "responsive to the periodic operation "of said code following "relay at *said fixed rate"for energizing"said'detector "relay.

2.:Apparatus for detecting the {presence 'of a movable *Object "such :as a vehicle in "a protected area, comprising "a loop' of insulated wire enclosing said area, a 'Wheatstone bridge circuit normally supplied with alternating current for 'comparing the electrical characteristics *of said "loop with 'those .of a balancing'imp'ed'ance to. detect varitions in the im'pedance'of'saidfloop due to th'e presence or a vehicle 'insaid area,.saidbridge circuitibeing .balancedwhen "saidfarea is unoccupied "but becoming unbalanced when "a vehicle occupiesthe. area, .a "codefollowing' relay deriving its energization from said :bridge circuit "and arranged to remainenerg'ized only solong'as said bridge is unbalanced, a code transmitter relay arranged v to unbalance lsaidflbrid'ge periodically regardless o'fth'e condition (if occupancy of said loop, a detector 1relay,-and meansior selectively energizing said detector relay in response to the periodic operation "of said code following relay. 3. Self-checking apparatus for detecting'when the impedance .o'f an electric circuit:.element is of a particular value, comprising a Wheatstone bridge'which'isbalanced only when said-circuit element is of said particular value andvis effectivelylincluded in one of itsarms, a source of current connected to the input ,terminals of @the bridge and constantly supplying current f a given "character thereto, a sensitive relay controlled :'by 'means responsive to current-of said given character derived from the output terminals of said bridge whereby said relay is maintained energized, when the bridge is unbalanced and releases when the bridge is substantially balanced, contact means operating periodically to vary the impedance of one of said arms to cause said relay to recurrently assume its released position in the event the impedance of said circuit element is substantially of said predetermined value and to then return to its energized position thereby checking the integrity of the bridge circuits, a-detector relay, and means controlled by said sensitive relay for maintaining said detector relay energized in response to the periodic changes :in the position'nf'said sensitive relay.

4. Self checking apparatus :for .detectingivarie ations: in :theximpedance ofcan electric-circuit element "comprising a detector? relay, :a "sensitive :16- lay, andaaWheatstone bridge having:inp1it iterminals :connected to :a source of .current in 2a given :character and :output terminals .for delivering ."current of :said character ".to a sensitive re'lay,;said bridge consisting of .four impedances one :of which includes said .TClICllit element :so proportioned ithatisaid sensitive relay :assumes its releasedjposition even though its icircuitris intact when said circuit element is being supplied :withcurrent :by :said bridge, provided :the impedance of said'circuitelement is of such value that .theibridge is balanced, contact means for unbalancing 'one arm of saidbridgeto render said :sensitiverelay responsive to the :current "of said .given character supplied to :the bridge to cause said relay toassume its energized position regardless .of the impedance of :said :circui-t element,'means for operating said contact means periodically, and i means selectively responsive 120 the periodic operation of said sensitive 'relay which results from the operation of said-contact means when the bridge is periodically balanced for energizing said detector relay.

'5. In combination withan electric ,circuitelement the impedance of which is subject to change from a'normal value, a-Wheatstone 'bridge ha-w ing two ratio .arms-anarm which includes said variable circuit element and one which includes a balancing impedance said bridge having its input terminals normaliy connectedto a source of current, a sensitive relay deriving its-energiza tion from connections to the output terminals of said bridge but which assumes its released position when'the bridge is balanced amovable contact in thecircuit -fcronearm only of said bridge which in one position enables the'bridge to "be "balanced and in-another position unbalancesthe bridge regardless of the impedance of said variable circuit element, means 'foropera'ting said movable contact periodica ly to cause the-periodic operation of said sensitive relay-provi'de'd said current of given character is continu-- ously supplied to thebridge and the characteristicscf said'variable circuit element asmeasured thereby are: substantially similar to those of said balancing impedance, a detector relay and-means dependent upon the periodic operation of said sensitive relay'for energizing said detector relay.

1611A system for detecting the intrusion of a movable object in "a 'protected space, comprising an extended bonducltor adjdining said space Tor creat'ing a fieldof force-which varies in'the presence of an object 'in'isaidspace when said I con ductor vis --supplied with alternating current, a Wheatstone bridge -ha'ving "its "input terminals connected 130 3 source of alternating cu'rrentfor comparing -*'the electrical characteristics of said conductor with those of a balancing impedance whereby said bridge may be balanced when said conductor is included in one of its arms, provided said space is unoccupied, a sensitive relay deriving its energization from the output terminals of said bridge but which assumes its released position even though its circuit is intact When the bridge is balanced, a movable contact in the circuit for one arm of said bridge which in one position enables the bridge to be balanced and in another position unbalances said bridge irrespective of the condition of occupancy of said space,

means for operating said movable cont'act periodic'ally, a detector relay, and means selectively responsive to the periodic operation of said sensitive relay for energizing said detector relay.

7. A system for detecting the intrusion of a movable object in a protected space, comprising an extended conductor adjoining said space for creating a field of force which varies in the presence of an object in said space when said conductor is supplied with alternating current, a Wheatstone bridge having its input terminals connected to a source of alternating current for comparing the electrical characteristics of said conductor with those of a balancing impedance whereby said bridge may be balanced when said conductor is included in one of its arms provided said space is unoccupied, a sensitive relay deriving its energization from the output terminals of said bridge but which assumes its released position even though its circuit is intact, when the bridge is balanced, a movable contact in the circuit for said conductor by which said conductor may be disconnected from said bridge to cause said sensitive relay to assume its energized position if its circuit is intact, irrespective of the condition of occupancy of said space, means for operating said movable contact periodically, a detector relay, and means dependent upon the periodic operation of said sensitive relay for maintaining said detector relay energized only as long as said space is unoccupied.

8. A system for detecting the presence of a movable object in a protected space, comprising a conductor arranged in the form of a loop surrounding at least a portion of said space to create a magnetic field therein which varies in the presence of an object in said space when said loop is energized by alternating current, a Wheatstone bridge having its input terminals connected to asource of alternating current, means comprising a movable contact for connecting said loop to said bridge to effect its energization and to-compare its impedance with that of a balancing impedance in said bridge, a sensitive relay deriving its energization from the output terminals of said bridge but which assumes its released position even though its circuit is intact, provided the impedance of said loop as compared with said balancing impedance indicates that said space is unoccupied, means for operating said movable contact periodically to indicate the balance of said bridge by the periodic energization of said sensitive relay, and a detector relay selectively responsive to the periodic operation of said sensitive relay for indicating the condition of occupancy of said space.

9. A system for detecting the presence of a movable object in a protected space, comprising a conductor arranged in the form of a loop surrounding at least a portion of said space to create a magnetic field therein which varies in the presence of an object in said space, when said loop is energized by alternating current, a Wheatstone 8, bridge having its input terminals connected to a source of alternating current for effecting the energization of said loop and for comparing its impedance with that of a balancing impedance in said bridge of such a value that the bridge is balanced when the space is unoccupied, an electron tube for detecting the potential difference at the output terminals of the bridge, asensitive relay maintained in its energized position by energy supplied by said tube except when said bridge is substantially balanced, means independent of the condition'of said space for periodically unbalancing said bridge whereby said relay alternately assumes its energized and released positions when said space is unoccupied but remains in its energized position when said space is occupied, and a detector relay which assumes its energized position in response to the periodic energization and release of said sensitive relay.

10. A system for indicating the presence of a movable object in a protected area, comprising a conductor energized by alternating current and arranged in the form of a loop to create a magnetic field in said area, a Wheatstone bridge having the source of said current connected to its input terminals and said loop included in one of its arms, the other arms of said bridge comprising fixed impedances of such value that the bridge is balanced when said area is unoccupied and becomes substantially unbalanced when a movable object enters said area, a sensitive relay responsive to the condition of energization of the. output terminals of the bridge, said relay assuming its energized position when the bridge is unbalanced by a movable object in said space and assuming its released position when the bridge is balanced, means for periodically unbalancing said bridge to effect the energization of said relay irrespective of the condition of occupancy of said space, a detector relay, means for maintaining said detector relay energized to indicate the unoccupied condition of said area in response to the alternate energization and release of said sensitive relay due to the periodic operation of said unbalancing means and indication means controlled by said detector relay.

GEORGE W. BAUGHMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,056,104 Kramer Mar. 18, 1913 1,633,302 Wyant June 21, 1927 1,773,472 Bossart Aug. 19, 1930 2,105,930 Reichard Aug. 8, 1944 2,355,395 Rubenstein Aug. 8, 1944 2,429,607 Capen Oct. 28, 1947 2,454,687 Baughman Nov. 23, 1948 

